Heronis Alexandrini spiritalium liber

appearing to us. For if anyone pours water into a vessel that appears empty, as much water as enters the vessel, just as much air will depart. Anyone can understand what has been said from this: for if someone were to push a vessel that appears empty upside down into water, and kept it upright, water will not enter into it, even if the whole thing were hidden. Thus it is clear that air, since it exists as a body, does not allow water to enter, for the reason that the whole place which is in the vessel is filled by it. If, therefore, someone were to pierce the bottom of the vessel, water would indeed enter into it through the mouth; but the air would exit through the hole. Again, before the bottom is pierced, if someone were to lift the upright vessel out of the water, turning it, they would see its entire inner surface to be free from moisture and clean, just as it was before it was submerged. Therefore, air is to be considered a body. Moreover, spirit original: "spiritus" (breath or movement of air) is made when it is moved. For spirit is nothing other than the motion of air. Therefore, through a vessel pierced at the bottom, and with water entering, if someone places a hand to the hole, they will feel...